1. Technical Field
The present invention relates to a device for synthesizing a high dynamic range image and a method thereof. More particularly, the present invention relates to a device and a method for synthesizing a high dynamic range image based on per-pixel exposure mapping.
2. Description of Related Art
Due to hardware limitation, a photosensitive element is unavoidably has its dynamic imaging range limited. For a scene containing lighter and darker parts that are excessively different in terms of brightness, in the case of a low dynamic range, the captured image may have the lighter parts shown as an expanse of whiteness and the darker parts shown as an expanse of blackness, making the captured image lose image details (such as information about contours and lines) in the extremely light and dark areas and thus fail to faithfully reflect the real scene.
For addressing this problem, many approaches have been proposed in order to improve dynamic range imaging. The images generated through these imaging approaches are usually referred to as HDRI (High Dynamic Range Imaging). A commonly adopted high dynamic range imaging technology involves adjusting a photographic equipment's parameters so as to capture images of an identical scene with different exposure values, and then synthesizing the captured images. Such image synthesis helps to keep the details of both the light and dark areas in the resultant image, thereby faithfully reproducing the original scene and in turn expanding the displayable dynamic range. This technology is extensively usable for, such as, shooting in high-contrast environments or welding masks to perform real-time weld seam tracking. In the latter case, the high-contrast source images captured during welding operation are processed and synthesized to allow the operator to find locations of welds through the display screen.
While the forgoing imaging scheme works when the shot subject matter is in a static state, for a subject matter moves during the image-capturing process, offset may exist between the images of the subject matter in two successive frames (depending on the movement velocity and the number of frames obtained every second) and such offset may be regarded as noise during imaging, thus leading to image distortion.
Additionally, since all pixels in each image are synthesized using the same exposure value as the benchmark, during tone mapping, depending on the brightness (Quantigraphic Measure), camera response function and noise interference of each pixel, the pixels having too high or too low brightness may be presented in the resultant image as over-exposed or under-exposed areas and fail to present details clearly due to high contrast. As a result, even the image processed by the high dynamic range imaging fails to present all the details, meaning that the existing technology needs to be improved for perfect tone mapping.